Hi cafe, I have played quite a bit with the ConstraintKinds extension, pretty cool. But I found a problem which I thought would be made better, plz correct me if I am wrong take a contrived example, class C B => B a where here B :: * -> Constraint, I think this definition is reasonable, since B does not appears in the first position of the context. Previously, we require acyclic class declarations since we don't have ConstraintKinds extension but now since type class could be abstracted, I think the definition above should be ok. the ghc-manual cited the program below is valid class C a where { op :: D b => a -> b -> b } class C a => D a where { ... } I think there are no reasons to reject class C B => B where (and this style is pretty useful in some cases) ... B :: * -> Constraint C :: (*->Constraint) -> Constraint Any comments are welcome -- Best, bob